单选题 The latest research on caloric restrictions shows that near-starvation diets may not be the Fountain of Youth.
Decades ago, in the 1930s, researchers found that animals that had been deprived of food seemed to live longer than rodents that were fed to satisfaction, raising the intriguing idea that maybe near-starvation was a good, rather than bad thing, for health. But the latest research conducted on close human cousins, rhesus monkeys, shows that the connection may not be as solid as once hoped. Published in the journal Nature, the results suggest that dramatically cutting back on daily calories—by 30%—does not help monkeys to live longer than those who ate normally. The restriction did help older monkeys to lower their levels of triglycerides, a risk factor for heart disease, but otherwise conferred no significant health or longevity benefit.
Caloric restriction may have its evolutionary roots as a survival mechanism, allowing species to survive on scraps when food is scarce in order to continue to reproduce. But that restriction only has lasting positive effects if the overall diet is a balanced one, which may not always be the case in conditions of famine. It"s possible the strategy developed as a way to protect species from consuming toxic plants or foods, when it wasn"t always obvious which sources were prohibited.
The study, begun in 1987 and one of the longest running trials to investigate the effects of caloric restriction, contradicts the only prior research conducted with rhesus monkeys, which found the opposite effect, highlighting the complex relationship between caloric processing and metabolic functions that contribute to aging and health. For example, the study"s lead author, Rafael de Cabo of the National Institute on Aging, notes that the effects of caloric restriction on the immune system may not be all good: some studies show slower wound healing and increased risk for infectious disease. In young animals, restricting calories also reduces fertility.
It"s not entirely clear why the two monkey studies had such varying results. Ricki Colman, a co-author of the first monkey study and an associate scientist at the Wisconsin National Primate Research Center, believes that the differences may reflect variance in the diets given to the animals in the two studies. "They may be modeling different things," she says, explaining that in her study, the control animals were allowed to eat freely while in the new research, both controls and those on the restricted diet were limited to specific maximum amounts. Her control animals, she says, may reflect more of a typical American diet, while the controls in the new research are more like people who already eat healthy amounts.
Indeed, the NIA study implies that the benefits of simply eating a balanced, healthy diet may provide as much life extension as dietary restrictions can produce. Even with the findings, however, some experts are still holding out hope that restricting calories may prove beneficial for certain health outcomes, specifically in combating cancer and heart disease. The question, of course, is how much restriction can you get away with in order to still get these benefits.

单选题 The new research has found that ______

单选题 In evolutionary terms, caloric restriction is considered to be ______

单选题 The old study on rhesus monkeys was different in that ______

单选题 Colman interprets the contradictory results by noting that ______

单选题 The new research would advise ______